A variety of different types of excavation machines have been developed for cutting drifts, tunnels, subterranean roadways and the like in which a rotatable head is mounted on an arm that is in turn movably mounted at a main frame so as to create a desired tunnel cross sectional profile. WO2012/156841, WO 2012/156842, WO 2010/050872, WO 2012/156884, WO2011/093777, DE 20 2111 050 143 U1. All described apparatus for mill cutting of rock and minerals in which a rotating cutting head forced into contact with the rock face as supported by a movable arm. In particular, WO 2012/156884 describes the cutting end of the machine in which the rotatable heads are capable of being raised and lowered vertically and deflecting in the lateral sideways direction by a small angle in an attempt to try enhance the cutting action.
WO 2014/090589 describes a machine for digging roadways tunnels and the like in which a plurality of cutting heads are movable to dig into the rock face via a pivoting arcuate cutting path. US 2003/0230925 describes a rock excavator having a cutter head mounting a plurality of annular disc cutters suitable to operate in an undercutting mode.
Furthermore, it has been observed that conventional cutting machines are not optimised to cut hard rock having a strength typically beyond 120 MPa whilst creating a tunnel or subterranean cavity safely and reliably of desired cross sectional configuration. Accordingly, what is required is a cutting machine that addresses these problems.
Further, different types of devices for the installation of rock bolts are known in the art. Such devices comprise a supporting structure carrying a bolting unit, wherein the bolting unit is configured for drilling a drill hole and moving a rock bolt into a rock face in order to secure the roof of a tunnel or subterranean roadway. Optional a mesh structure covering the rock face is used for additional protection against roof fall.
In order to provide sufficient support for a roof of a tunnel in most applications the bolts used to secure the mesh structure have to be nearly half of the tunnel width or tunnel height, respectively.
Since the devices for the installation of rock bolts often form part of a cutting apparatus suitable for creating tunnels and subterranean roadways, the bolting process must not lead to a delay of the generation of the tunnel. In order to accelerate the installation of the rock bolts, devices have been developed which are able to simultaneously drill two or more installation holes into the rock face.
DE 1 807 972 A describes a drilling device comprising a pair of drilling units, wherein the drilling units may be rotated about a common axis of rotation. However, the drilling holes that are created by means of this device are not orientated in radial direction to the common axis of rotation.
This leads to the fact that the installed bolts have a reduced effective anchor length due to their offset to the radial direction. The reduced effective anchor length results in the need of longer bolts in order to provide a sufficient support for the roof of the tunnel.